Prometheus Complete Overhaul

[blakehatch]

Should migrate to otel and target for after 0.3.0

[adam-singer]

In this context it might be worth watching https://github.com/tokio-rs/tokio-metrics. Currently the package is marked as unstable so I think we should avoid it, the building blocks and runtime support does match the async framework we use. Probably should be a separate issue to be filed on it, but re-eval when we look at metrics again.